<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>栅格系统</title>
    <script src="jquery-3.4.1.js"></script>
    <script src="bootstrap.js"></script>
    <link rel="stylesheet" href="bootstrap.css">
</head>
<style>
    div{
        border: 1.5px solid #000;
    }
</style>
<body>
<div class="container">
    <div class="row">
        <div>
            <div class="col-md-3 col-xs-6">1</div>
            <div class="col-md-3 col-xs-6">2</div>
            <div class="col-md-3 col-xs-6">3</div>
            <div class="col-md-3 col-xs-6">4</div>
        </div>
    </div>
</div>

</body>
</html>